Animal Nutrition and Digestion Notes

How do animals obtain food?
Animals are heterotrophs, obtaining nutrients and energy from food through various adaptations like filter feeding, detritivory, carnivory, and herbivory.
How does digestion occur in animals?
Digestion in animals occurs either intracellularly within specialized cells or extracellularly in digestive systems like gastrovascular cavities or digestive tracts, involving mechanical and chemical breakdown and absorption of nutrients.
How are mouthparts adapted for different diets?
Mouthparts are adapted for different diets; carnivores have sharp structures for capturing and slicing meat, while herbivores have mouthparts for rasping or grinding plant material.

Intracellular digestion: Digestion inside specialized cells, with nutrients passed to other cells by diffusion.
Extracellular digestion: Food is broken down outside cells in theh digestive system and then absorbed.
Gastrovascular cavity: An interior body space in some animals where tissues carry out digestive and circulatory functions, having a single opening for ingestion and waste expulsion.
Digestive tract: A tube with two openings where food is digested; it moves in one direction, entering through the mouth and exiting as waste through the anus.
Rumen: A specialized pouch in some herbivores, like cattle, where symbiotic bacteria digest cellulose.

Animals are heterotrophs, obtaining nutrients and energy from food.
Adaptations for feeding styles are a significant part of what makes animals interesting.
An animal's appearance and behavior depend on what and how it eats, and vice versa.

Filter feeders strain food from water.
They catch algae and small animals using modified gills or other structures as nets.
Many invertebrate filter feeders are small or colonial, living in a single spot as adults.
Vertebrate filter feeders like whale sharks and blue whales are huge and feed while swimming.

Detritus is decaying plant and animal material.
Detritivores feed on detritus, obtaining extra nutrients from bacteria, algae, and other microorganisms on and around it.
Earthworms and various aquatic worms and crustaceans are essential detritivores in many ecosystems.

Carnivores eat other animals.
Mammalian carnivores like wolves use teeth, claws, speed, or stealth to capture prey.
Carnivorous invertebrates, such as cnidarians (using poison-tipped darts) and spiders (using venomous fangs), can be terrifying.

Herbivores eat plants or parts of plants in terrestrial and aquatic habitats.
Some, like locusts and cattle, eat leaves, which are low in nutritional content, difficult to digest, and can contain poisons or hard particles.
Others, like birds and many mammals, eat seeds or fruits, which are often filled with energy-rich compounds.

Parasites live within or on a host organism, feeding on tissues or body fluids.
Some are nuisances, but many cause serious diseases in humans, livestock, and crop plants.
Parasitic flatworms and roundworms afflict millions, particularly in the tropics.

In mutualistic relationships, both participants benefit.
Reef-building corals depend on symbiotic algae in their tissues for energy.
Algae capture solar energy, recycle nutrients, and help corals lay down calcium carbonate skeletons.
Algae gain nutrition from coral wastes and protection from algae eaters.
Animals that eat wood or plant leaves rely on microbial symbionts in their guts to digest cellulose.

A scientist studied the time needed for a carnivorous animal to digest animal protein.
Egg white (animal protein) was placed in a test tube with hydrochloric acid, water, and pepsin (an enzyme that digests protein).
The rate of digestion was measured over 24 hours.

Food must be digested and absorbed to make energy and nutrients available.
Some invertebrates use intracellular digestion, but many animals use extracellular digestion.
A variety of digestive systems are shown in Figure 27-2.

The simplest animals, like sponges, digest food inside specialized cells, passing nutrients to other cells by diffusion.

Most more-complex animals rely on extracellular digestion, where food is broken down outside cells in a digestive system and then absorbed.

Some animals have an interior body space whose tissues carry out digestive and circulatory functions.
Cnidarians have a gastrovascular cavity with a single opening for ingestion and waste expulsion.
Cells lining the cavity secrete enzymes and absorb digested food.
Other cells surround food particles and digest them in vacuoles.
Nutrients are transported to cells throughout the body.

Many invertebrates and all vertebrates digest food in a tube called a digestive tract, which has two openings.
Food moves in one direction, entering through the mouth and exiting as waste through the anus.
One-way digestive tracts often have specialized structures like a stomach and intestines that perform different tasks.
The digestive tract is like an assembly line that breaks down food one step at a time.
The mouth may secrete digestive enzymes to start digestion.
Mechanical digestion may occur as mouthparts or a gizzard breaks food into small pieces.
Chemical digestion begins or continues in a stomach with digestive enzymes.
Chemical breakdown continues in the intestines, aided by secretions from organs like the liver or pancreas.
Intestines also absorb nutrients.

Indigestible material is expelled as feces through the single digestive opening or the anus.

Mouthparts and digestive systems are adapted to the physical and chemical characteristics of different foods.
Adaptations to meat and plant leaves are examined.

Carnivores and herbivores have different mouthparts related to the physical characteristics of meat and plant leaves.

Carnivores have sharp mouthparts or structures to capture, hold, and slice food.
Carnivorous mammals like wolves have sharp teeth to grab, tear, and slice food.
Jaw bones and muscles are adapted for up-and-down movements to chop meat into small pieces.

Herbivores have mouthparts adapted to rasping or grinding.
They need to tear plant cell walls and expose their contents.
Herbivorous invertebrates have mouthparts that grind and pulverize leaf tissues.
Herbivorous mammals like horses have front teeth and muscular lips for grabbing and pulling leaves, and flattened molars for grinding leaves to a pulp.
Jaw bones and muscles are adapted for side-to-side grinding movements.

Carnivorous invertebrates and vertebrates have short digestive tracts that produce fast-acting, meat-digesting enzymes that digest most cell types in animal tissues.
No animal produces enzymes to break down cellulose in plant tissue.
Some herbivores have long intestines or specialized pouches with microbial symbionts that digest cellulose.
Cattle have a rumen, where symbiotic bacteria digest cellulose.
Ruminants regurgitate partially digested food from the rumen, chew it again, and reswallow it (chewing the cud).